The value attribute of the selectItems tag is bound to the newsletters managed bean,
which is configured in the application configuration resource file. The newsletters managed bean is configured as a list:

As shown in the managed-bean element, the UISelectItems component is a collection of SelectItem instances.
See Initializing Array and List Properties for
more information on configuring collections as beans.

You can also create the list corresponding to a UISelectMany or UISelectOne component programmatically in the backing bean. See Writing Bean Properties for information on how to
write a backing bean property corresponding to a UISelectMany or UISelectOne component.

The arguments to the SelectItem constructor are:

An Object representing the value of the
item

A String representing the label that displays
in the UISelectMany component on the page